1. Field of the Invention
The present invention relates to the recovery of petroleum by injection of fluids to cause its displacement toward production wells.
2. Description of the Prior Art
The use of micellar systems for the displacement of oils is taught by a variety of United States patents, of which the following are exemplary.
Oil external miceller systems for oil recovery are mentioned in U.S. Pat. No. 3,261,399 to Coppel, U.S. Pat. No. 3,226,570 to Gogarty, U.S. Pat. No. 3,301,325 to Gogarty and Olsen, U.S. Pat. No. 3,476,184 to Davis and U.S. Pat. No. 3,497,008 to Jones and Roszelle. Water-external micellar systems are mentioned in U.S. Pat. No. 3,599,715 to Roszelle, U.S. Pat. No. 3,506,070 to Jones and U.S. Pat. No. 3,506,071 to Jones. Both water-external and oil-external micellar systems are mentioned in U.S. Pat. No. 3,254,714 to Gogarty and Olsen, U.S. Pat. No. 3,376,925 to Coppel, and U.S. Pat. No. 3,455,385 to Gogarty.
The literature contains many other patents and unpatented articles on this subject.
The test methods for differentiating oil-in-water and water-in-oil micellar systems have great importance in characterizing the various systems. The various tests include the dye solubility method, the phase dilution method, the conductivity method, the fluorescence method, the wetting of filter paper; all taught in more detail in Emulsions: Theory and Practice (Reinhold Publishing Corp., New York), particularly at pages 413-426 and in the references cited therein. The importance of a combination of miscibility data together with conductivity data is taught by a letter "On Determining the Continuous Phase in Microemulsions" by K. D. Dreher and R. D. Sydansk in the December, 1971, Journal of Petroleum Technology, pages 437 and 438. This letter also states that ". . . a system with the characteristics of a water-external micellar solutiion can exist in equilibrium with excess aqueous phase." and supports this with experimental evidence.
Later experimentation has led to the discovery that these anomalous or "intermediate micellar systems" which are substantially immiscible with either oil or water provide enhanced recovery of oil in the presence of water, either connate or remaining from previous water flooding. The increased oil recovery caused by the employment of intermediate micellar systems by the present invention has obvious economic advantages. The resistance of these systems to the uptake of both water and oil within the formation permits them to travel great distances through the formation while retaining efficiency as oil displacement fluids. This stability, then, permits wider spacing between injection and production wells with a consequent reduction in drilling costs required for secondary-type (including tertiary) recovery.